In a data processing system, such as a system which includes a plurality of point of sale terminals and a central processing unit, it is often required that data which is entered from an input device such as a keyboard or a UPC (universal product code) scanner be sent from a data concentrator or a point of entry terminal to a central processing unit (CPU) for processing. Data resulting from the processing may then be returned to the data concentrator or point of entry terminal. For example, one system in which such an arrangement may be required is the Class 7000 point of sale system, manufactured and marketed by NCR Corporation, Dayton, Ohio.
The processing within the central processing unit may comprise, for example, data verification, processing of the input data, and building of output messages to the terminal. The data verification may include a determination of whether the data has been entered in proper sequence, whether the length of the data entered meets specified criteria, and whether sufficient information has been received to permit further processing. Processing of the input data may include price look-up for universal product code items from a disk subsystem. The building of output messages may comprise the assembly of one or more messages to be displayed on devices present at the point of sale terminal and the assembly of messages to be printed on printer devices controlled by the terminal.
It is important that such point of sale systems be able to accomplish their data processing functions as quickly as possible, since in some point of sale installations, such as supermarkets, a typical customer transaction may consist of forty or more items that must be individually entered at a point of sale terminal, and that are each processed by the central processing unit. The inclusion of a larger number of point of sale terminals in such a system usually results in an increase in the amount of time required to process a single item, due to the increased activity involving the disk system and the increasing requirements imposed upon the resources of the central processing unit.
At times, it may become necessary to monitor and measure the time required to process a data entry from the time that the entry is made at the POS terminal until a data response is received at the terminal from the central processing unit. This time is usually referred to as the response time of the system. These time measurements can be used to determine the effect of adding more terminals to the system. The measurements can also be used to determine the effect that any changes made in the system software have, and whether any software changes are required in order to provide better system performance.
System performance can be measured in a number of ways. One way is by use of external measuring and monitoring devices. These devices are customarily separate stand-alone type instruments, which are often costly and which often require extensive training for an operator to use effectively. Usually a single device is used to monitor activity of a single terminal or of the central processing unit. A second way to monitor performance is by monitoring of input/output within the central processing unit by use of central processing resources such as processing time and storage facilities, which means that such resources are not available for other purposes.